A cataract is an opacity of the lens of the eye. Cataracts may be congenital or may occur as a result of trauma or, less commonly, systemic disease. Senile cataract is by far the most common type, and most people over sixty have some degree of lens opacity.
A cataractous lens, or one which has become partially or wholly opaque, sometimes requires removal from the eye, and replacement with an intraocular lens. Whether to remove the lens depends upon a variety of factors taken into consideration by the ophthalmic surgeon. If a decision is made to remove the lens, the surgeon has a choice of several techniques. In some instances a lens implant may be placed in the eye without removing the natural lens of the eye.
In the conventional cataract extraction technique, a conjunctive flap is formed by making an incision in the conjunctiva so that it can be moved back to expose the sclera of the eye at the corneal border. In order to obtain access to the cataractous lens, which is located behind the cornea, an incision is made extending around the cornea in the limbus area, a short distance (between about zero to two millimeters) from the periphery of the cornea and extending between approximately 3.0 and 6.0 mm. One of the more desirable types of incisions is a multiplane incision, or "stepped" incision, in which a first cut, in a first plane, extends only partially through the cornea. This partial thickness incision has been referred to as a "cataract groove. " Second, and sometimes third, cuts, in second and third planes, are then made to enter the anterior chamber for access to the lens.
The first incision typically extends to a depth of approximately one-half the thickness of the wall of the eye globe, and is made by use of a scalpel blade, razor blade, or other instrument, held freehand either perpendicular to the wall of the eye globe or at an angle to it. The first incision may be enlarged with either a scissor, keratome, or other blade implement. Once the entire incision is completed, the cornea can be lifted or retracted to gain access to the anterior chamber. The cataractous lens can then be removed.
The multiplane, or "stepped, " incision has a number of advantages over an incision which lies in a single plane and extends through the full thickness of the eye into the anterior chamber. With a single plane incision, there is a tendency for fluid to leak through the incision, requiring the use of sutures. With a stepped incision, however, there is a tendency for-the incision to seal itself, obviating the need for sutures.
Prior to the present invention, the first cut in a stepped incision has been formed freehand by the surgeon. No matter how skilled the surgeon may be, it is difficult to make the cut with precision. No two incisions will ever be exactly the same, and hence results and post operative effects vary. In addition, the surgeon often encounters difficulty in completing the full incision, since the cutting edge is usually supported in a holder gripped by the surgeon in one hand while he stabilizes the globe of the eye with a fixator or forceps in the other hand. Accordingly, it is necessary for the surgeon to both rotate the globe of the eye using the fixator in one hand while rotating the position of the cutting edge with the other hand. The surgeon often finds himself in an awkward position and unable to complete the cut in a single sweeping motion. This can result in a cut which is not smooth, or may not be positioned in the desired location.
It is an object of the present invention to provide a cutting device for making a stepped incision in a single linear, reciprocal stroke of a guided cutting edge, so that it is unnecessary for a surgeon to make the cut freehand.
The invention reduces the level of surgical skill required, and provides a more consistent, better sealing, and faster healing incision.